In recent years, techniques of separating a target material from a mixture and analyzing the target material have been used in a wide variety of applications. Particularly, these techniques have been used for medical research on separation of viruses and cancer cells. In treating cancer patients, circulating tumor cells (CTCs) are detected in the blood of patients and observed in order to determine the survival probability, diagnose cancer recurrence, and measure the effects of cancer treatment.
CTCs are regarded as the major factor contributing to death in cancer patients. Most cancer patients die of metastasis of cancer cells from primary tissues or organs to other tissues or organs not directly connected therebetween. Thus, early detection and monitoring of metastasis is a critical factor for the survival of cancer patients. In addition, CTCs may be used for detecting metastasis. In general, cancers metastasize through blood, and thus, CTCs may be used as a marker to diagnose the metastasis of cancer cells. However, although CTCs exist in blood, it is very difficult to accurately identify their existence. Even though CTCs are identified in blood, the amount for analyzing the characteristics of the detected CTCs is limited because selectively separating CTCs from erythrocytes and leukocytes contained in blood is limited.
One of the related arts for separating CTCs discloses a method of separating blood into erythrocytes, leukocytes, CTCs, and serum via a density gradient condition to manually isolate a desired layer. However, according to this method, leukocytes and CTCs are not separated from each other but exist in a mixture, and thus, the separation efficiency of CTCs from leukocytes is small.
Other related arts disclose cell margination and multi-orifice separation based on fluid dynamics principles. The former is a technology whereby the number of small cells such as erythrocytes is relatively reduced and the number of other cells is increased by using a phenomenon which occurs in actual blood vessels in which small particles gather in the inner part of the blood vessels and large particles move outside. The latter is a principle whereby a channel along which a fluid flows has an expanded tube section to respectively gather large particles and small particles outside and in the middle of the channel according to the Reynolds number. However, it is difficult to selectively separate a desired target cell from blood by using this principle, and there is limitation in treating a volume of several ml because the fluid flow rate is slow. Also, it is necessary to dilute a fluid by several hundred times in order to control the Reynolds number, and thus, there is a limitation in that samples of several hundred ml should be actually treated. Accordingly, there still remains a need for a method of efficiently separating a target matter such as CTCs from a mixture such as blood.